The invention generically relates to aqueous dispersions based on a polyurethane synthetic resin which has been obtained by reacting a hydroxyl-containing polyester with a diisocyanate and reacting the product with a compound which contains at least two groups which react with isocyanate groups and at least one group capable of anion formation, and with a chain-lengthening agent.
Aqueous dispersions of this type are known. German Offenlegungsschrift No. 1,495,745 describes a process for preparing aqueous emulsifierless polyurethane latices based on polyurethane materials prepared from polyhydroxyl compounds, polyisocyanates and, if appropriate, chain-lengthening agents.
The existing dispersions of this generic type have the disadvantage that if they are dried physically without the addition of a hardening agent they do not give solvent-resistant coatings. The coatings are sensitive, in particular to acetone but also to other solvents, which severely impairs their usefulness.